This report summarizes the 2021 fiscal year (FY21) status of ongoing borehole heater tests in salt funded by the disposal research and development (R&D) program of the Office of Spent Fuel & Waste Science and Technology (SFWST) of the US Department of Energy’s Office of Nuclear Energy’s (DOE-NE) Office of Spent Fuel and Waste Disposition (SFWD). This report satisfies SFWST milestone M2SF- 21SN010303052 by summarizing test activities and data collected during FY21. The Brine Availability Test in Salt (BATS) is fielded in a pair of similar arrays of horizontal boreholes in an experimental area at the Waste Isolation Pilot Plant (WIPP). One array is heated, the other unheated. Each array consists of 14 boreholes, including a central borehole with gas circulation to measure water production, a cement seal exposure test, thermocouples to measure temperature, electrodes to infer resistivity, a packer-isolated borehole to add tracers, fiber optics to measure temperature and strain, and piezoelectric transducers to measure acoustic emissions. The key new data collected during FY21 include a series of gas tracer tests (BATS phase 1b), a pair of liquid tracer tests (BATS phase 1c), and data collected under ambient conditions (including a period with limited access due to the ongoing pandemic) since BATS phase 1a in 2020. A comparison of heated and unheated gas tracer test results clearly shows a decrease in permeability of the salt upon heating (i.e., thermal expansion closes fractures, which reduces permeability).
In response to personal protective equipment (PPE) shortages in the United States due to the Coronavirus Disease 2019, two models of N95 respirators were evaluated for reuse after gamma radiation sterilization. Gamma sterilization is attractive for PPE reuse because it can sterilize large quantities of material through hermetically sealed packaging, providing safety and logistic benefits. The Gamma Irradiation Facility at Sandia National Laboratories was used to irradiate N95 filtering facepiece respirators to a sterilization dose of 25 kGy(tissue). Aerosol particle filtration performance testing and electrostatic field measurements were used to determine the efficacy of the respirators after irradiation. Both respirator models exhibited statistically significant decreases in particle filtering efficiencies and electrostatic potential after irradiation. The largest decrease in capture efficiency was 40–50% and peaked near the 200 nm particle size. The key contribution of this effort is correlating the electrostatic potential change of individual filtration layer of the respirator with the decrease filtration efficiency after irradiation. This observation occurred in both variations of N95 respirator that we tested. Electrostatic potential measurement of the filtration layer is a key indicator for predicting filtration efficiency loss.
Shortages of N95 respirators for use by medical personnel have driven consideration of novel conservation strategies, including decontamination for reuse and extended use. Decontamination methods listed as promising by the Centers for Disease Control and Prevention (CDC) (vaporous hydrogen peroxide (VHP), wet heat, ultraviolet irradiation (UVI)) and several methods considered for low resource environments (bleach, isopropyl alcohol and detergent/soap) were studied for two commonly used surgical N95 respirators (3M™ 1860 and 1870+ Aura™). Although N95 filtration performance depends on the electrostatically charged electret filtration layer, the impact of decontamination on this layer is largely unexplored. As such, respirator performance following decontamination was assessed based on the fit, filtration efficiency, and pressure drop, along with the relationship between (1) surface charge of the electret layer, and (2) elastic properties of the straps. Decontamination with VHP, wet heat, UVI, and bleach did not degrade fit and filtration performance or electret charge. Isopropyl alcohol and soap significantly degraded fit, filtration performance, and electret charge. Pressure drop across the respirators was unchanged. Modest degradation of N95 strap elasticity was observed in mechanical fatigue testing, a model for repeated donnings and doffings. CDC recommended decontamination methods including VHP, wet heat, and UV light did not degrade N95 respirator fit or filtration performance in these tests. Extended use of N95 respirators may degrade strap elasticity, but a loss of face seal integrity should be apparent during user seal checks. NIOSH recommends performing user seal checks after every donning to detect loss of appropriate fit. Decontamination methods which degrade electret charge such as alcohols or detergents should not be used on N95 respirators. The loss of N95 performance due to electret degradation would not be apparent to a respirator user or evident during a negative pressure user seal check.
N95 respirators became scarce to the general public in mid-to-late March of 2020 due to the SARS-CoV-2 epidemic. By mid-April of 2020, most states in the United States were requiring face coverings to be worn while in public enclosed places and in busy outdoor areas where groups of people were in close proximity. Many resorted to cloth masks, homemade masks, procedure masks obtained through online purchases, and other ad-hoc means. Thus, there was and still is a need to determine the aerosol filtration efficacy of commonly available materials that can be used for homemade mask construction. This study focused on non- woven polymeric fabrics that are readily available for homemade mask construction. The conclusion of this study is that non-woven materials that carry a high electric charge or those that can easily acquire charge had the highest aerosol filtration efficiency per unit of pressure drop. Future work should examine a wider variety of these materials and determine the maximum pressure drop that a nominal homemade mask can withstand before a significant portion of airflow is diverted around the mask. More broadly, a better understanding of the charge state on non-woven materials and impact of that charge state on filtration efficiency is needed.
Epoxies and resins can require careful temperature sensing and control in order to monitor and prevent degradation. To sense the temperature inside a mold, it is desirable to utilize a small, wireless sensing element. In this paper, we describe a new architecture for wireless temperature sensing and closed-loop temperature control of exothermic polymers. This architecture is the first to utilize magnetic field estimates of the temperature of permanent magnets within a temperature feedback control loop. We further improve performance and applicability by demonstrating sensing performance at relevant temperatures, incorporating a cure estimator, and implementing a nonlinear temperature controller. This novel architecture enables unique experimental results featuring closed-loop control of an exothermic resin without any physical connection to the inside of the mold. In this paper, we describe each of the unique features of this approach, including magnetic field-based temperature sensing, extended Kalman filtering for cure state estimation, and nonlinear feedback control over time-varying temperature trajectories. We use experimental results to demonstrate how low-cost permanent magnets can provide wireless temperature sensing up to ∼ 90°C. In addition, we use a polymer cure-control testbed to illustrate how internal temperature sensing can provide improved temperature control over both short and long time-scales. This wireless temperature sensing and control architecture holds value for a range of manufacturing applications.
Vibration sensing is critical for a variety of applications from structural fatigue monitoring to understanding the modes of airplane wings. In particular, remote sensing techniques are needed for measuring the vibrations of multiple points simultaneously, assessing vibrations inside opaque metal vessels, and sensing through smoke clouds and other optically challenging environments. In this paper, we propose a method which measures high-frequency displacements remotely using changes in the magnetic field generated by permanent magnets. We leverage the unique nature of vibration tracking and use a calibrated local model technique developed specifically to improve the frequency-domain estimation accuracy. The results show that two-dimensional local models surpass the dipole model in tracking high-frequency motions. A theoretical basis for understanding the effects of electronic noise and error due to correlated variables is generated in order to predict the performance of experiments prior to implementation. Simultaneous measurements of up to three independent vibrating components are shown. The relative accuracy of the magnet-based displacement tracking with respect to the video tracking ranges from 40 to 190 μ m when the maximum displacements approach ±5 mm and when sensor-to-magnet distances vary from 25 to 36 mm. Last, vibration sensing inside an opaque metal vessel and mode shape changes due to damage on an aluminum beam are also studied using the wireless permanent-magnet vibration sensing scheme.
Radionuclides and heavy metals easily sorb onto colloids. This phenomenon can have a beneficial impact on environmental clean-up activities if one is trying to scavenge hazardous elements from soil for example. On the other hand, it can have a negative impact in cases where one is trying to immobilize these hazardous elements and keep them isolated from the public. Such is the case in the field of radioactive waste disposal. Colloids in the aqueous phase in a radioactive waste repository could facilitate transport of contaminants including radioactive nuclides. Salt formations have been recommended for nuclear waste isolation since the 1950's by the U.S. National Academy of Science. In this capacity, salt formations are ideal for isolation of radioactive waste. However, salt formations contain brine (the aqueous phase), and colloids could possibly be present. If present in the brines associated with salt formations, colloids are highly relevant to the isolation safety concept for radioactive waste. The Waste Isolation Pilot Plant (WIPP) in southeast New Mexico is a premier example where a salt formation is being used as the primary isolation barrier for radioactive waste. WIPP is a U.S. Department of Energy geological repository for the permanent disposal of defenserelated transuranic (TRU) waste. In addition to the geological barrier that the bedded salt formation provides, an engineered barrier of MgO added to the disposal rooms is used in WIPP. Industrial-grade MgO, consisting mainly of the mineral periclase, is in fact the only engineered barrier certified by the U.S. Environmental Protection Agency (EPA) for emplacement in the WIPP. Of interest, an Mg(OH)2-based engineered barrier consisting mainly of the mineral brucite is to be employed in the Asse repository in Germany. The Asse repository is located in a domal salt formation and is another example of using salt formations for disposal of radioactive waste. Should colloids be present in salt formations, they would facilitate transport of contaminants including actinides. In the case of colloids derived from emplaced MgO, it is the hydration and carbonation products that are of interest. These colloids could possibly form under conditions relevant in particular to the WIPP. In this chapter, we report a systematic experimental study performed at Sandia National Laboratories in Carlsbad, New Mexico, related to the WIPP engineered barrier, MgO. The aim of this work is to confirm the presence or absence of mineral fragment colloids related to MgO in high ionic strength solutions (brines). The results from such a study provides information about the stability of colloids in high ionic strength solutions in general, not just for the WIPP. We evaluated the possible formation of mineral fragment colloids using two approaches. The first approach is an analysis of long-term MgO hydration and carbonation experiments performed at Sandia National Laboratories (SNL) as a function of equivalent pore sizes. The MgO hydration products include Mg(OH)2 (brucite) and Mg3 Cl(OH)5•4H2O (phase 5), and the carbonation product includes Mg5(CO3)4(OH)2•4H2O (hydromagnesite). All these phases contain magnesium. Therefore, if mineral fragment colloids of these hydration and carbonation products were formed in the SNL experiments mentioned above, magnesium concentrations in the filtrate from the experiments would show a dependence on ultrafiltration. In other words, there would be a decrease in magnesium concentrations as a function of ultrafiltration with decreasing molecular weight (MW) cut-offs for the filtration. Therefore, we performed ultrafiltration on solution samples from the SNL hydration and carbonation experiments as a function of equivalent pore size. We filtered solutions using a series of MW cut-off filters at 100 kD, 50 kD, 30 kD and 10 kD. Our results demonstrate that the magnesium concentrations remain constant with decreasing MW cutoffs, implying the absence of mineral fragment colloids. The second approach uses spiked Cs+ to indicate the possible presence of mineral fragment colloids. Cs+ is easily absorbed by colloids. Therefore, we added Cs+ to a subset of SNL MgO hydration and carbonation experiments. Again, we filtered the solutions with a series of MW cut-off filters at 100 kD, 50 kD, 30 kD and 10 kD. This time we measured the concentrations of Cs. The concentrations of Cs do not change as a function of MW cut-offs, indicating the absence of colloids from MgO hydration and carbonation products. Therefore, both approaches demonstrate the absence of mineral fragment colloids from MgO hydration and carbonation products. Based on our experimental results, we acknowledge that mineral fragment colloids were not formed in the SNL MgO hydration and carbonation experiments, and we further conclude that high ionic strength solutions associated with salt formations prevent the formation of mineral fragment colloids. This is due to the fact that the high ionic strength solutions associated with salt formations have high concentrations of both monovalent and divalent metal ions that are orders of magnitude higher than the critical coagulation concentrations for mineral fragment colloids. The absence of mineral fragment colloids in high ionic strength solutions implies that contributions from mineral fragment colloids to the total mobile source term of radionuclides in a salt repository are minimal.
Here, a solubility model is presented for ferrous iron hydroxide (Fe(OH)2(s)), hibbingite (Fe2Cl(OH)3(s)), siderite (FeCO3(s)), and chukanovite (Fe2CO3(OH)2(s)). The Pitzer activity coefficient equation was utilized in developing the model to account for the excess free energies of aqueous species in the background solutions of high ionic strength. Solubility limiting minerals were analyzed before and after experiments using X-ray diffraction. Formation of Fe(OH)2(s) was observed in the experiments that were initiated with Fe2Cl(OH)3(s) in Na2SO4 solution. Coexistence of siderite and chukanovite was observed in the experiments in Na2CO3 + NaCl solutions. Two equilibrium constants that had been reported by us for the dissolution of Fe(OH)2(s) and Fe2Cl(OH)3(s) (Nemer et al.) were rederived in this paper, using newer thermodynamic data selected from the literature to maintain internal consistency of the series of our data analyses in preparation, including this paper. Three additional equilibrium constants for the following reactions were determined in this paper: dissolution of siderite and chukanovite and dissociation of the aqueous species Fe(CO3)2–2. Five Pitzer interaction parameters were derived in this paper: β(0), β(1), and Cφ parameters for the species pair Fe+2/SO4–2; β(0) and β(1) parameters for the species pair Na+/Fe(CO3)2–2. Our model predicts that, among the four inorganic ferrous iron minerals, siderite is the stable mineral in two WIPP-related brines (WIPP: Waste Isolation Pilot Plant), i.e., GWB and ERDA6 (Brush and Domski), and the electrochemical equilibrium between elemental iron and siderite provides a low oxygen fugacity (10–91.2 atm) that can keep the actinides at their lowest oxidation states. (Nemer et al., Brush and Domski; references numbered 1 and 2 in the main text).